Process for making a linear alpha-olefin oligomer using a heat exchanger

ABSTRACT

The invention pertains to a process for making a linear alpha-olefin oligomer in a reactor comprising a liquid and a gas phase, comprising the steps of catalytically oligomerizing ethylene in the presence of an iron complex of a 2,6-bis(arylimino)pyridine derivative, to an alpha-olefin oligomer under release of heat, and removing the heat with a heat exchanger, which is not in direct contact with the liquid phase, using at least part of the gas phase as a coolant medium. The invention further relates to an apparatus to perform said process.

FIELD OF THE INVENTION

[0001] The invention pertains to a process for making a linearalpha-olefin oligomer from ethylene in a reactor having a liquid and agas phase, in the presence of a catalyst.

BACKGROUND OF THE INVENTION

[0002] Various processes are known for the production of higher linearalpha olefins (See, for example, D. Vogt, Oligomerisation of ethylene tohigher a-olefins in Applied Homogeneous Catalysis with OrganometallicCompounds, Ed. B. Cornils, W. A. Herrmann, 2nd Edition, Vol. 1, Ch.2.3.1.3, page 240-253, Wiley-VCH 2002). These commercial processesafford either a Poisson or Schulz-Flory oligomer product distribution.In such a process, a wide range of oligomers is typically made.

[0003] In WO 02/00339, WO 02/12151, WO 02/06192, WO 02/28805, WO01/58874, and WO 99/02472 novel Fe-based ethylene oligomerizationcatalysts are described that show high activity and high selectivitytowards linear alpha-olefins. These catalysts, which are incorporated byreference, are based on iron complexes of a selected2,6-pyridinedicarboxaldehyde bisimine or a selected 2,6-diacylpyridinebisimine.

[0004] In the present invention the term “bis-(arylimino)-pyridine” isused to describe both classes of ligands. Alpha-olefin oligomers arecompounds or a mixture of compounds with the general formulaH₂C═CH—(CH₂CH₂)_(n)H wherein n is an integer of 1 or greater. In sucholigomers the alpha-olefin oligomer is usually a mixture of alpha-olefinoligomers with a mean number n from 1 to 20, preferably from 2 to 10.Alpha-olefin oligomers prepared according to the process of the presentinvention preferably have an average molecular weight between about 50and about 350, more preferably between about 60 and about 280, even morepreferably between about 80 and about 210.

[0005] The reaction of ethylene in the presence of the above ironcomplex is usually run in the liquid phase in a well-mixed reactor,typically using an aprotic organic solvent. This reaction generates alarge amount of heat, which should be removed. As described in WO02/06192 it is preferred to install a plurality of small reactors incombination with several heat exchangers to help provide sufficientcooling capacity for the reactor system. The process temperature, whichusually is between about 35° C. and about 90° C., more preferablybetween about 35° C. and about 75° C., affects the cost of manufactureof the alpha-olefins in several ways. The higher the temperature thesmaller the heat exchangers which have to be applied to the reactor(s),which generally lowers cost. The decay of the active oligomerizationcatalyst increases with increasing temperature. It is found that maximumvolumetric production of alpha-olefins coupled with good absoluteproductivity of the catalyst usually occurs in the range of about 45° C.to about 75° C., so this temperature range is preferred. Finally, thetemperature also affects the bubble point pressure, the amount ofethylene in the liquid phase, and the catalyst selectivity. The higherthe temperature the higher the pressure needed to maintain catalystselectivity, which increases capital cost of the manufacturing plantbecause of, for example, the need for thicker vessels and largercompressors to attain higher ethylene pressures. Higher pressure alsoincreases energy costs.

[0006] The amount of ethylene (ethene) oligomerization catalyst used inthe reaction will preferably be the maximum permitted by the coolingcapacity of the reactor(s) and the ethylene mass transfer from the gasto the liquid phase. Catalyst may be added to the first reactor only orto one or more subsequent reactors in series. Differing amounts ofcatalyst may be added to each reactor. The oligomerization is quiteexothermic, about 100 kJ/mole of ethylene oligomerized, and as suchcooling will usually be applied to the reactor(s) to maintain thedesired process temperature while maintaining high volumetricproductivity of the reactor(s).

[0007] In the prior art cooling is accomplished by running cooling tubesthrough the liquid in the interior of one or more of the reactors tocool the contents. Another method of cooling is to have one or more heatexchangers external to the reactors and connected to the reactors by aliquid loop to cool the reactor contents. These external heat exchangersmay be typical shell and tube exchangers. The reactors may also bejacketed with a cooling jacket. Some or all of the feeds to some or allof the reactors may be cooled to allow the sensible heat of theingredients to cool the reactors. All these liquid cooling methods,however, suffer from the disadvantage of wax and polyethylene fouling ofthe coolers, which necessitates regular shut down of the reactor toallow cleaning of the coolers. Furthermore, wax and polyethylene foulingmay increase the paraffinicity of the solvent.

SUMMARY OF THE INVENTION

[0008] It would be advantageous to devise a process without the abovedisadvantages. It has now been found that linear alpha-olefin oligomerscan be made in a reactor comprising a liquid and a gas phase, comprisingthe steps of catalytically oligomerizing ethylene in the presence of aniron complex of a 2,6-bis(arylimino)pyridine derivative, to analpha-olefin oligomer with an average molecular weight between about 50and about 350 under release of heat, and removing the heat with a heatexchanger, which is not in direct contact with the liquid phase, usingat least part of the gas phase as a coolant medium.

[0009] This method provides a cooling system having its cooling elementsoutside the liquid reaction medium. Since wax and polyethylene have highboiling points, deposit of wax and polyethylene can no longer occur, andfouling of the heat exchanger is effectively prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] The invention is illustrated by the following Figures, which arenot meant to limit the invention in any way, showing a scheme of anapparatus that can be used for performing the process of the invention.

[0011]FIG. 1 is a scheme of an apparatus for performing the methodaccording to the invention with the heat exchanger positioned outsidethe reactor.

[0012]FIG. 2 is a scheme of an apparatus for performing the methodaccording to the invention with the heat exchanger positioned inside thereactor.

DETAILED DESCRIPTION OF THE INVENTION

[0013] The heat exchanger according to this invention is a conventionaltype, such as a shell- and tube-type, and the like. The heat exchangeris internally cooled with conventional cooling fluids, like water,ammonia, Freon® coolant, and the like. The reaction heat causes thesolvents, reactants, and/or reaction products, which are present in thereaction medium, to evaporate and subsequently to be cooled by the heatexchanger, after which it works as a coolant medium for the reactor. Theheat exchanger can be placed inside or outside the reactor. When theheat exchanger is placed inside the reactor it is preferred that somecondensation occurs on the heat exchanger surface. When the heatexchanger is placed outside the reactor, it is preferred to apply aforced circulation of the reactor coolant medium from the gas phase ofthe reactor through heat exchanger(s), compressor(s)/pump(s) andoptionally a gas-liquid separator back to the liquid phase of thereactor. Additionally, this will improve the mixing in the reactor.After cooling the reactor coolant medium in this loop, some condensationcan occur. This allows application of a separate gas and liquid returnto the reactor using a gas-liquid separator. Furthermore, it is possibleto deliberately remove (part of) this liquid phase from this gas-liquidseparator and route this directly to the product work-up section.Finally, if full condensation occurs, return of this liquid to thereactor can be achieved by a pump instead of a compressor, which lowerscosts. This reactor coolant medium is selected from an alkane, alkene,and aromatic compound, and mixtures thereof, preferably propane,n-pentane, isopentane, ethylene, 1-butene, o-, m-, and p-xylene, andtoluene, and mixtures thereof.

[0014] An additional advantage of the present process is the possibilityto apply only one reactor, because the efficiency and the lack offouling no longer necessitates the use of a plurality of small reactors.This adds considerably to the lowering of costs of the oligomerizationprocess.

[0015] The iron complexes of the 2,6-bis(arylimino)pyridine type thatcan be used in the above process are known in the art, and are describedin WO 02/00339, WO 02/12151, WO 02/06192, WO 02/28805, WO 01/58874, andWO 99/02472. Any of these complexes can be used. Best results, however,are obtained with such iron complexes wherein one of the aryl moietiesof the 2,6-bis(arylimino)pyridine derivative is 2,6-disubstituted withthe group CH₂R or C₂H₅R, wherein R is selected from H, F, andsubstituted or unsubstituted aryl, preferably selected from H and F, andthe other aryl moiety is 2,6-unsubstituted, or wherein both arylmoieties of the 2,6-bis(arylimino)pyridine derivative are2,6-disubstituted with F or Cl.

[0016] Particularly useful are the 2,6-bis(arylimino)pyridinederivatives with the formula:

[0017] wherein

[0018] R1 is H or CH₃;

[0019] R2 is H, tert-butyl or phenyl; and

[0020] R3 is H, tert-butyl or OR′ wherein R′ stands for CH₃,

[0021] Si(CH₃)₃ or eicosyl (C₂₀H₄₁); and

[0022] The term “aryl” means an aromatic group, such as phenyl,naphthyl, thienyl, pyridyl, pyrrolyl, and the like. Phenyl is thepreferred aryl group. Preferred phenyl groups are substituted with CH₃,tert-butyl, F, or OR′ wherein R′ stands for CH₃ or Si(CH₃)₃.

[0023] In a preferred embodiment an aluminum-based co-catalyst,preferably a methylaluminoxane, is added to the liquid phase. Where aco-catalyst such as an alkylaluminum compound is required or preferredfor the active catalyst species, an iron complex of a2,6-bis(arylimino)pyridine derivative, such as a complex of the2,6-bis(arylimino)pyridine derivative with FeCl₂, may be reacted with analkylaluminum compound, preferably an aluminoxane, to form an activeethylene oligomerization species. Specific alkylaluminum compoundsinclude methylaluminoxane (which is an oligomer with the general formula(MeAlO)_(n)), (C₂H₅)₂AlC₁, C₂H₅AlCl₂, (C₂H₅)₃Al and ((CH₃)₂CHCH₂)₃Al. Aparticularly preferred aluminoxane is methyl aluminoxane. The ratio ofaluminum (as alkylaluminum compound) to iron (as a complex) in theoligomerization may be about 10 to about 10,000.

[0024] Another preferred component of the catalyst systems herein is asecond co-catalyst compound selected from formula ZnR′₂ wherein each R′,which may be the same or different, is selected from hydrogen,optionally substituted C₁-C₂₀ hydrocarbyl, phenyl, F, Cl, Br, I, SR″,NR″₂, OH, OR″, CN, NC wherein R″, which within the same molecule may bethe same or different, is C₁-C₂₀ hydrocarbyl.

[0025] In preferred catalyst systems herein, the second co-catalystcompound is ZnR′₂ wherein R′ is C₁-C₂₀ hydrocarbyl, more preferablyC₁-C₂₀ alkyl, even more preferably C₁-C₆ alkyl. Suitable alkyl groupsinclude methyl, ethyl, propyl, butyl, and the like. It is especiallypreferred that the R′ group is a C₁-C₃ alkyl, especially ethyl.

[0026] The second co-catalyst is particularly valuable in combinationwith the aluminium-based co-catalyst for increasing the selectivity oflinear alpha olefins in ethylene oligomerization reactions, anddecreasing the amount of unwanted by-products such as branched olefins,internal olefins, 2,2-disubstituted olefins, and dienes.

[0027] It has been noted that particularly high selectivity of linearalpha olefins is achieved when the molar ratio of the metal of thealuminium-based co-catalyst to the metal of the second co-catalyst is inthe range of from about 5:1 to about 1:5, preferably from about 3:1 toabout 1:3, more preferably from about 2:1 to about 1:2 and especiallyabout 1:1.

[0028] It is possible to add further optional components to the catalystsystems herein, for example, Lewis acids and bases such as thosedisclosed in WO02/28805.

[0029] The active catalyst system may be formed by mixing together theiron complex of a 2,6-bis(arylimino)pyridine derivative or a mixture ofthe iron acetylacetonate complex and the appropriate2,6-bis(arylimino)pyridine derivative (ligand), first co-catalystcompound, second co-catalyst compound and any optional additionalcompounds, preferably in a solvent.

[0030] An important item in the capital cost of this manufacturing plantand in its cost of operation is the amount of reactor coolant mediumthat must be recycled in the process. Recycling of a gaseous reactorcoolant medium often involves recompression to feed one or more of thereactors. Compressors and associated equipment add greatly to capitaland operational costs. In the present method the coolant medium ispreferably selected to completely dissolve ethylene. In this case thecoolant medium only requires a single reactor and a condenser, whereas asimple recycle pump is sufficient. Thus expensive recycling, such as theuse of an expensive recycle blower, is no longer required, which addsfurther to the advantages of the present method.

[0031]FIG. 1 shows a reactor 2 with a liquid phase 3 and a gas phase 4being in equilibrium through gas/liquid interface 12. The liquid phasecomprises ethylene, the nickel, palladium, cobalt, titanium, zirconium,hafnium, vanadium, chromium, molybdenum, or tungsten complex of a2,6-bis(arylimino)pyridine derivative, alpha-olefin oligomer, andoptionally solvents and auxiliaries such as a co-catalyst. The optionalsolvents are selected as to dissolve ethylene. The reactor 2 contains aninlet 10 through which the reactor feed 1 (usually ethylene) isintroduced into the reactor 2, a gas outlet 11, and a reactor bottomoutlet 9. In the embodiment of FIG. 1, outlet is connected through aconduit 14 to heat exchanger 5 a, which is connected through conduit 15to gas-liquid separator 6. If necessary, conduit 15 may contain acompressor 7 a. Gas-liquid separator 6 has an outlet for transportingthe liquid, optionally through a pump 8, to obtain a pressurized liquidstream 17 that is recycled via conduit 19 to reactor 2. The gas leavesthe gas-liquid separator 6 through conduit 16, which may optionallycomprise compressor 7 b and/or heat exchanger 5 b, to obtain a cooledgas stream 18 that is recycled to reactor 2. If no condensation occursin conduit 15, gas-liquid separator 6, and pump 8 are redundant and maybe deleted. In that case conduit 15 can directly be connected tocompressor 7 b and/or heat exchanger 5 b, if present, or to conduit 19.Reactor 2 may contain an optional entrainment separator 13.

[0032]FIG. 2 shows another embodiment of the invention. In thisembodiment the reactor feed 1 is introduced into the reactor 2 throughinlet 10. The liquid phase 3 in the reactor is in equilibrium with thegas phase 4 through gas/liquid interface 12. In the section of thereactor containing the gas phase 4, a heat exchanger 20 is placed, whichis not in contact with the liquid phase 3. The section of the gas phase4 may optionally contain an entrainment separator 13. The heat exchanger20 cools the gas, after which at least part of the gas condenses and thecooled condensate falls down from the surface of the heat exchanger 20into the liquid phase 3, thereby cooling the liquid medium. The reactionproduct may then be discharged from the reactor through the reactorbottom outlet 9.

[0033] Hence, according to a further aspect of the present inventionthere is provided an apparatus for performing the process of makinglinear alpha-olefin oligomer described above, comprising a reactor,which can accommodate a liquid and a gas phase, an inlet through whichthe reactor feed can be introduced into the reactor, a reactor bottomoutlet to remove the oligomer, and a heat exchanger, which is positionedin the gas phase to condense the gas and allow the condensate to falltherefrom to cool the liquid phase, and optionally, an entrainmentseparator, and/or a gas-liquid separator.

We claim:
 1. A process for making a linear alpha-olefin oligomer in areactor comprising a liquid and a gas phase, comprising the steps ofcatalytically oligomerizing ethylene in the presence of an iron complexof a 2,6-bis(arylimino)pyridine derivative, to an alpha-olefin oligomerunder release of heat, and removing the heat with a heat exchanger whichis not in direct contact with the liquid phase, using at least part ofthe gas phase as a coolant medium.
 2. The process of claim 1 wherein analuminum-based co-catalyst is added to the liquid phase.
 3. The processof claim 2 wherein the aluminum-based co-catalyst is an aluminoxaneselected from the group consisting of methyl aluminoxane, alkyl-modifiedmethyl aluminoxane, and mixtures thereof.
 4. The process of claim 3wherein the aluminum-based co-catalyst is a methyl aluminoxane.
 5. Theprocess of claim 1 wherein the oligomer is an alpha-olefin oligomer withan average molecular weight between about 50 and about
 350. 6. Theprocess of claim 5 wherein the average molecular weight is between about60 and about
 280. 7. The process of claim 6 wherein the averagemolecular weight is between about 80 and about
 210. 8. The process ofclaim 2 to which is added a second co-catalyst compound which comprisesone or more compounds of the formula ZnR′₂ wherein each R′, which may bethe same or different, is selected from hydrogen, optionally substitutedC₁-C₂₀ hydrocarbyl, phenyl, F, Cl, Br, I, SR″, NR″₂, OH, OR″, CN, NCwherein R″, which within the same molecule may the same or different, isC₁-C₂₀ hydrocarbyl.
 9. The process of claim 8 wherein R′ is C₁-C₂₀hydrocarbyl.
 10. The process of claim 9 wherein R′ is C₁-C₂₀ alkyl. 11.The process of claim 10 wherein R′ is C₁-C₆ alkyl.
 12. The process ofclaim 11 wherein R′ is ethyl.
 13. The process of claim 1 wherein one ofthe aryl moieties of the 2,6-bis(arylimino)pyridine derivative is2,6-disubstituted with the group CH₂R or C₂H₅R, wherein R is selectedfrom H and F, and the other aryl moiety is 2,6-unsubstituted, or whereinboth aryl moieties of the 2,6-bis(arylimino)pyridine derivative are2,6-disubstituted with F or Cl.
 14. The process of claim 1 wherein the2,6-bis(arylimino)pyridine derivative has the formula:

wherein R1 is H or CH₃; R2 is H, tert-butyl or phenyl and R3 is H,tert-butyl or OR′ wherein R′ stands for CH₃, Si(CH₃)₃ or eicosyl(C₂oH₄₁); or


15. The process of claim 1 wherein the coolant medium is selected fromthe group consisting of an alkane, an alkene, and an aromatic compound,and mixtures thereof.
 16. The process of claim 1 wherein the coolantmedium is selected from the group consisting of propane, n-pentane,isopentane, ethylene, 1-butene, o-, m-, and p-xylene, and toluene, andmixtures thereof.
 17. An apparatus for performing the process of makinglinear alpha-olefin oligomer of claim 1 comprising a reactor which canaccommodate a liquid phase and a gas phase, an inlet through which thereactor feed is introduced into the reactor, a reactor bottom outletthrough which the oligomer is removed, a heat exchanger which ispositioned in the gas phase to condense the gas and allow the condensateto fall therefrom to cool the liquid phase thereby cooling the liquid,and optionally, a gas outlet and/or an entrainment separator.
 18. Theapparatus of claim 17 wherein a gas entrainment separator which ispositioned in the gas phase.
 19. An apparatus for performing the processof making linear alpha-olefin oligomer of claim 1 comprising 1) areactor which can accommodate a liquid phase and a gas phase, a reactorfeed inlet, a gas outlet, and a reactor bottom outlet for the reactionproducts, 2) a heat exchanger which is positioned outside of thereactor, receives gas from the reactor gas outlet, and cools the gas,wherein said gas flows from the heat exchanger through a first gasconduit where part of the gas condenses, 3) a gas-liquid separator whichhas a gas outlet and a liquid outlet, receives gas and liquid from theheat exchanger, and separates gas, which exits the separator through asecond gas conduit and is recycled to the reactor, from liquid, whichexits the separator through a liquid conduit and is recycled to thereactor.
 20. The apparatus of claim 19 further comprising a compressorbetween the heat exchanger and the gas-liquid separator.
 21. Theapparatus of claim 20 further comprising a pump in the liquid conduit.22. The apparatus of claim 20 further comprising a compressor and/or aheat exchanger in the second gas conduit.
 23. The apparatus of claim 20further comprising an entrainment separator in the reactor in the gasphase.
 24. An apparatus for performing the process of making linearalpha-olefin oligomer of claim 1 comprising 1) a reactor which canaccommodate a liquid phase and a gas phase, a reactor feed inlet, a gasoutlet, and a reactor bottom outlet for the reaction products, and 2) aheat exchanger which is positioned outside of the reactor, receives gasfrom the reactor gas outlet, and cools the gas, wherein said gas flowsfrom the heat exchanger through a gas conduit and is recycled to thereactor.
 25. The apparatus of claim 15 further comprising a compressorand/or a heat exchanger in the gas conduit.